Abnormal neuronal activity, injury, and aging exert physical stress on the nervous system, leading to neuronal dysfunction and degeneration. NMNATs (nicotinamide mononucleotide adenylyl transferases) play a central role in maintaining neuronal integrity following a wide range of environmental challenges. Neuroprotection by NMNAT overexpression appears to be widespread as its overexpression delays axonopathy following nerve injury and ameliorates neurodegeneration in several neurodegenerative models, including Charcot-Marie- Tooth disease and tauopathies. The broad protective effects of NMNAT suggest that it protects at a step common to numerous neurodegenerative processes and raises the possibility that manipulating NMNAT expression or activity may provide a unique opportunity to develop therapies for treating many neurodegenerative diseases. There are three mammalian NMNAT homologs, NMNAT1-3, with NMNAT2 being the most labile isoform. Impairing NMNAT2 function leads to axonal degeneration in the peripheral nervous system. Our preliminary studies revealed that NMNAT2 levels in Alzheimer Disease (AD) patient cerebral cortex are reduced by more than 60%. Using the FTDP-17 tauopathy animal model, rTg4510 mice, we found that NMNAT2 levels were substantially decreased prior to the onset of neurodegeneration. Most importantly, exogenous Nmnat2 expression in rTg4510 hippocampus reduced neurodegeneration and the accumulation of toxic tau species. We hypothesize that NMNAT2 is required to maintain neural function and to reduce toxic protein accumulation in many different contexts. The goal of this proposal is to use cultured mouse and human cells as well as transgenic mouse models to elucidate the mechanisms underlying NMNAT2 protection against neurodegeneration and maintaining the health of mature neurons.